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D.C. Elfving and E.C. Lougheed

In three trials over 3 years, foliar BA applications for fruitlet thinning of `Empire' apple (Malus domestica Borkh.) trees produced small and inconsistent effects on flesh firmness at harvest and after air storage. Soluble solids concentrations at harvest and after air storage were consistently increased by BA alone or together with GA4+7 [Promalin (PR)], and were also increased by CB in one trial. Starch hydrolysis was slightly delayed by BA applications in 1990. Ethylene evolution at harvest was increased by NAA in 1988 and slightly increased by PR applied 29 days after full bloom (DAFB) in 1990, while poststorage ethylene evolution was stimulated by BA and PR treatments in 1990 except BA at 29 DAFB. Incidence of poststorage disorders was low and largely uninfluenced by thinning treatments. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; BA plus gibberellins A4 and A7 (GA 4+7) [Promalin (PR)]; 1-naphthaleneacetic acid (NAA); 1-naphthalenyl methylcarbamate [carbaryl (CB)].

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A. Dale, D.C. Elfving and C. Chandler

Day-neutral strawberries produce runners less freely than June-bearing strawberries, which leads to reduced production in nursery fields. To alleviate this, a series of experiments were done to test how effectively benzyladenine (BA) and gibberellic acid (GA3) increased runner production. In greenhouse tests with the varieties `Tribute' and `Selva' and in field trials with `Selva', the combination of BA and GA3 consistently increased runner production in day-neutral strawberries, but not alone. Runner production increased linearly with BA dosage to 1800 ppm. GA3 produced very elongated internodes at high dosages, which led to fewer daughter plants in the field. Twelve-hundred ppm BA and 300 ppm GA3 are recommended as suitable concentrations to induce runnering both in the field and greenhouse.

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Patrick Gushing and Gerald Klingaman

Four bulb sizes of Hippeastrum hybridum `Appleblossom' were twin-scale propagated, soaked in 0, 0.01, 0.1, and 0.5 g·liter–1 of benzyladenine (BA), and incubated at 15, 20, 25C and a fluctuating temperature of 31C day, 21C night. Bulbil numbers were recorded following incubation and leaf emergence after bulbils were planted. Eight weeks after bulbils were planted, bulb diameter and leaf numbers were observed. BA application had no effect on bulbil initiation. However, bulbil formation per twin-scale cutting increased as temperature (up to 25C) and mother bulb diameter increased. Bulbil diameter and survival of bulbils increased as incubation temperature increased up to 20C. After planting bulbils, leaf emergence was hastened as bulb size decreased.

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V.E. Emongor, D.P. Murr, J.T.A Proctor and E.C. Lougheed

Field trials at Cambridge Research Station, Ontario, Canada, studied the thinning effect of benzyladenine (BA) on eighteen-year-old “Empire” apple trees. At 16 days after full bloom (fruit diameter 12.87 mm) whole trees were hand sprayed to drip point with BA (0, 100, or 200 mg.1-1). Untreated control trees were compared with treated and hand thinned trees. BA significantly reduced crop load on “Empire”. The thinning response to BA was linear, with recommended thinning occurring at 200 mg.1-1. At harvest, fruit weight, size (diameter and length), flesh firmness and soluble solids concentration, chlorophyll and anthocyanin contents, and seed number were increased by BA treatments. BA had no effect on fruit L:D ratio, internal ethylene concentration, maturity, and the onset of the respiratory climacteric, but significantly reduced respiration at harvest. BA also reduced ethylene production and ACC content at harvest, though the reduction was not significant. Although firmness of BA-treated fruit was significantly higher at harvest, upon storage for 1 month at 0-0.5°C and 90-95% RH the firmness advantage was lost BA shows potential as a thinner of “Empire” apple and has advantage of increasing fruit weight and size, since “Empire” is a relatively small apple compared to other commercial cultivars.

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Len Burkhart and Martin Meyer Jr.

Selected cultivars of redbud (Cercis canadensis L.) and related Cercis species are usually propagated by grafting, but the success rate is low and other problems can be associated with the rootstock. Micropropagation would solve many of these problems. Shoots from a 25 year-old redbud were collected during July 1989 and established in vitro on modified MS medium. Shoots proliferated poorly with lower concentrations of Benzyladenine (BA) and high concentrations of BA caused shoot tip abortion. Similar problems with red-silver hybrid maples were solved by the use of Thidiazuron (TZ) in the medium. Established 2 cm redbud shoots were treated with TZ (0, 0.05, and 0.1 uM) and BA (0, 1 and 5 uM) in a factorial arrangement to test for shoot proliferation. After 4 weeks of the treatment with 0.1 uM TZ and 5 uM BA, mean shoot number was 4.6 compared to 1.1 shoots with no BA or TZ in the medium. Further experiments with rooting treatments will be presented.

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Tracie K. Matsumoto

Flowering of Miltoniopsis orchids is influenced by a combination of cool temperatures and short photoperiod. To determine if application of plant growth regulators could promote flowering without the need for costly structural modification to control photoperiod or temperature, we used drenches of gibberellic acid (GA3) (2.5 or 5 mm), N6-benzyladenine (BA) (25 or 50 mm) alone or in combination. BA (25 or 50 mm) treatments promoted new vegetative shoots and decreased the number of plants with inflorescences compared to the untreated control plants. This reduction of flowering and increased vegetative shoot production was alleviated by the addition of GA3 in combination with BA. However, the number of plants with inflorescences remained less than the control. GA3 hastened Miltoniopsis inflorescence emergence during the first flowering season by 10.9 to 14.9 days for Bert Field `Eileen' and by 48.7 days for Rouge `Akatsuka'. The number of `Eileen' inflorescences produced per plant increased from 2.2 to 3.0 with 2.5 mm GA3 treatment. Flower deformities were not observed in the GA3 treated plants, and flower size and inflorescence length were unaffected by the GA3 treatment.

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Mark H. Brand

Although it is commonly recommended that shoot tip cultures be initiated from actively growing shoots, it has been demonstrated that shoot tips collected during the period of rapid shoot extension fail to produce shoot proliferating cultures. Shoot tips of Halesia Carolina and Malus `Golden Delicious' were collected at 2 week intervals from budbreak to summer dormancy and placed on medium containing 0, 4.5, 11.0, 22.5 and 44.5 uM benzyladenine (BA) to determine if elevated BA concentrations could overcome seasonal patterns of shoot proliferation potential (SPP). Both species reached maximum SPP 4 weeks post-budbreak (PBB), and exhibited a second window of high SPP during weeks 10 and 12. Elevated BA concentrations failed to overcome poor SPP exhibited by shoot tips harvested 6 to 8 weeks PBB. Shoot tips collected at 10 to 12 weeks PBB responded more favorably to higher exogenous BA concentrations than shoot tips collected at 2, 4, 6, or 8 weeks PBB. It appears as though seasonal fluctuations in SPP involve other endogenous factors in addition to cytokinins.

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Royal D. Heins, Thomas F. Wallace Jr. and Susan S. Han

Chlorosis of Easter lily (Lilium longiflorum) lower leaves causes significant economic loss. Lily plants growing in 15-cm pots were sprayed 30, 60, or 90 days after emergence or at 60 and 90 days after emergence with 25 to 100 ppm each of benzyladenine and GA4+7 from Promalin (Abbott Chemical Co.) and were grown pot-to-pot until flower. Chlorotic leaf count at flower decreased as Promalin concentration increased; plants sprayed at 60 days had the smallest chlorotic leaf count. Chlorotic leaves at flower varied from 28% for control plants to 10% for plants sprayed with 100 ppm at 60 days and from 36% to 17% 3 weeks later, respectively. The Promalin sprays promoted significant stem elongation, but differences in height at flower were only 2 cm. Plants sprayed with 100 ppm at 30 days averaged one deformed flower per plant; plants sprayed at 60 days and 60 and 90 days averaged 0.0 and 0.1 deformed flower per plant, respectively. Additional trials in which only the lower part of the plant was sprayed prevented any chlorotic leaves without any significant effect on final height or flower bud quality.

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Richard McAvoy and Bernard Bible

Bract necrosis (BN) in poinsettia is thought to be caused by a localized calcium deficiency in the margins of bracts. Both calcium and silicate sprays can suppress the post-anthesis development of BN if applied repeatedly during bract development. However, studies conducted in 1993 and 1994, with BN-susceptible scions (`Supjibi') grafted onto either `Supjibi' rootstock or the BN-resistant `Annette Hegg Dark Red' (AHDR) rootstock, failed to support the calcium hypothesis. In these studies, higher calcium concentrations were found in the margins of `Supjibi' bracts on `Supjibi' rootstock, then in `Supjibi' bracts on `AHDR' rootstock, even thought the incidence of BN was highest on plants with `Supjibi' rootstock. These studies suggested that non-nutritional factors (possibly hormonal factors) may play a role in BN. In 1995, `Supjibi' plants were produced in the greenhouse, and at initial anthesis, were sprayed once with either deionized (DI) water, benzyladenine (BA) (100 ppm), or daminozide (2000 ppm). At initial anthesis, plants in all treatment groups showed a low level of BN (0.75% of bracts with symptoms). Four weeks after initial anthesis, 18.5% of bracts on DI water sprayed plants and 38.7% of bracts on daminozide treated plants had developed BN; but BA treated plants developed BN on only 1% of bracts. At final harvest (38 days after treatments were applied), BN was evident on 3.4% of BA-treated bracts, 28.7% of DI-treated bracts, and 46.3% of daminozide-sprayed bracts.

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Duane W. Greene, Wesley R. Autio, Jeffrey A. Erf and Zhongyuan Y. Mao

BA thinned apple (Malus domestica Borkh.) fruits when applied to either the leaves or the fruit, although it was much more effective when applied to the leaves. BA increased fruit size independent of its effects on reducing crop load, but only when applied directly to the fruit. When applied to one of two fruit in a cluster, BA had no influence on abscission, fruit size, or fruit characteristics of the adjacent nontreated fruit. BA reduced fruit flesh Ca only on treated fruit and the response was inversely proportional to the increase in fruit size. More than 60% of the BA applied to a fruit was absorbed during 24 hours, and this amount was considerably larger than penetration through either the abaxial or adaxial leaf surface. BA treatments that thinned also increased ethylene production linearly in both leaves and fruit 24 hours after application, but the magnitude of increase was not considered large enough to be the primary cause for thinning. BA thinned spurs with two or three fruit more than spurs with one fruit, and it did not selectively thin to just one fruit per cluster. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)].